Developer compositions and their use in electrolytic electrophotography



prll l, 19,69 D. K, MEYER ETAL 3,436,321

DEVELOPER coMPosI'rIoNs AND THEIR usE IN ELEc'rRoLYTIcELECTROPHOTOGEAPHY Filed Sept. 13, 1966 Sheet of 2 .6 .a /.0 z e 06 Pil. EXPOSUE /Nl/E/vros o/vaza KME-rik 19055975 01.55

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Aprll l, 1969 D. K. MEYER ET Ax. 3,436,321

DEVELOPER COMPOSITIONS AND THEIR USE IN ELECTROLYTIC ELECTROPHOTOGRAPHY Filed sept. 13, 196e sheet Z of 2 .4 .6 .a a /2 f4 vL 06 62. EXPUJURF United States Patent() 3,436,321 DEVELOPER COMPOSITIONS AND THEIR USE IN ELECTROLYTIC ELECTROPHOTOGRAPHY Donald K. Meyer, West St. Paul, and Robert F. Coles,

North St. Paul, Minn., assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed Sept. 13, 1966, Ser. No. 579,114 Int. Cl. G03g 9/00 U.S. Cl. 204-18 This invention relates to novel developer compositions for use in electrolytic electrophotography. In one aspect this invention relates to an aqueous composition containing two or more developer materials which can be electrodeposted simultaneously in a wide range of continuously variable color density without a change of hue.

In electrolytic electrophotography a photoconductive copysheet having a strongly photoconductive layer on an electrically conductive substrate may be exposed to a light image and then electrolytically developed with the electrically conductive substrate connected as one electrode, preferably the cathode, and with the surface of the photoconductive layer in contact with a suitable developer solution which will effect a color change on the light struck areas of the copysheet surface. Such a process is described in U.S. 3,010,883. Particularly preferred color developers, such as those described in U.S. 3,172,826 and 3,172,827, may be utilized in multiple step processes to provide full color, continuous tone prints. Although black can be produced by the successive electrodeposition of cyan, magenta and yellow dyes, it is frequently desirable to electrodeposit a separate black image in a single step, and this may be achieved by using a developer containing dispersed carbon particles or a developer containing a silver salt.

To obtain developer dyestuffs which have the desired light absorption characteristics can be extremely diicult or impractical. Although it is possible to mix dyestutfs to obtain a desired color, dyestufs tend to electrodeposit at varying rates from such an admixture, producing an undesirable change of hue over the normal density range. If magenta, cyan and yellow dyestuffs are admixed to .produce a black color, the problem of differing electrodeposition rates is even more acute. Indeed the electrodeposition characteristics of a dyestulf admixture is generally not predictable from the electrodeposition rates and D log E curves of the individual dyestuffs therein. As a result, a good continuous gray scale is usually obtained by methods other than by using a combination of three dyestutfs in a single developer solution. Unfortunately, satisfactory black dyestuffs capable of rendering a neutral gray scale have not been found.

It is accordingly an object of this invention to provide an electrolytic electrophotographic developer solution having two or more dyestuffs which can be simultaneously electrodeposited onto a photoconductive copysheet without `a significant hue change over the density ranges used.

Still another object of this invention is to provide a multidyestulf electrolytic electrophotographic developer solution which can be used to electrodeposit a continuous gray scale of' photographic quality.

A further object of this invention is to provide an electrolytic electrophotographic developer of a desired color by admixing two or more dyestuffs.

Most electrolytically useful colored dyestulfs vary widely in their rates of electrolytic deposition, depending on such factors as chemical structure, concentration, development voltage and current, etc. Even under a given set of conditions, because the rate of deposition varies with the exposure, the plot of density (D) and log exposure (log E) is not a straight line. As would therefore be ex- 6 Claims pected, mixing developer dyestufls generally results in images of varying hue and unpredictable quality.

In accordance with this invention it has been found that two or more dyestulfs may be electrolytically deposited from an admixture without the abovementioned disadvantages, even though the individual dyestuffs may differ widely in their D log E curves. This effect appears to be generally independent of the size of the molecule and the chemical structure of the chromophoric group. Such dyestuffs have the formula wherein D is a chromogenic radical, R is an alkyl radical having from 6 to 12 carbon atoms, R is methyl or ethyl, n is 2` or 3, m is 2 or 3 and p is 0 or 1, where the controlling solubility characteristics of said dyestulf is attributable to the recited polyamine group. The chromogenic radical D may contain solubilizing groups, such as sulfonic acid, provided the effect of the polyamine group on the solubility is substantially retained, and the dyestuff is not rendered soluble in alkaline media. Thus, the dyestuffs of this invention `are soluble in acidic media, particularly at a pH below about 6, but are insoluble in alkaline media- The chromogenic radical D is preferably selected from the following classes: azo, anthraquinone, anthrapyridone, phthalocyanine, quinacridone, thioindigo and xanthene. Preferably, the recited polyamine radical is linked to the chromogenic nucleus through a methylene, polymethylene, carbonyl or sulfonyl bridging radical. Dyestuffs of this class have 'been disclosed in U.S. 3,- 172,827. Any two or more dyestulfs of the above formula maybe used together in aqueous acidic media in the form of their amine salts. The relative concentration of the respective dyestuffs is not generally critical and the effect is observed with wide ratios of the dye components (e.g., 9/1 to 1/9 weight ratio of two dyestuls in admixture), although optimum results (i.e., no significant change of color or hue in the toe or shoulder or intermediate portions of the D log E curve) may be obtained within certain concentration ratios of the specific dyestuffs used. The total dyestuffs concentration in the solution is generally in the range of 0.1 to 5% by weight.

To illustrate the invention a variety of representative dyestulfs within the above formula were mixed in a single aqeuous acidic solution and electrolytically deposited by the following procedure. In all instances the dyestulfs were utilized in amine salt form and were at least partially soluble in the aqueous acidic media. Each dyestulf was used as a 1-weight percent solution in dilute acid (pH 3-5.5), as indicated in U.S. Patent No. 3,172,827. Equal amounts of the dye solutions were then mixed together to form a mixture which could be electrolytically plated onto panchromatically sensitized photoconductive copysheets to obtain a variation in color gradation without significant change of hue through out the useful density range, frequently up to a density of 2.5. The photoconductive copysheets used contained photoconductive zinc oxide in a styrene-butadiene copolymeric binder (6/1 weight ratio of ZnO to binder). The sheets were exposed through a 0-3 neutral density Wedge and were developed for one second at 50 volts D.C. with the copysheet connected as cathode, using an apparatus of the type described in U.S. 3,172,827. The developed copysheets were then Washed with water and dried with an air jet. These sheets were coated with lacquer to protect the image and were then evaluated in a recording densitometer using red, green and blue filters successively. The curves were then examined to confirm the visual observation of the plated image and to establish the absence of any undesirable cross over points in the respective curves, an indication of nonuniform and variable plating.

nickel phthslocyanine As will be seen in the data in Table I the dystuls of this invention, though having widely diverse D log E curves when measured individually, electrodeposit uniformly without significant color change over the useful density range. Although the theoretical explanation for these phenomena is not fully understood, it appears that the polyamine substituents on the dyestuff primary controls the rate of electrodeposition when two or more of such dyestuffs are deposited from solution. The dyestufs em ployed in the illustrative examples are as follows:

Il H O copper phthaloeyanine copper phthalocyanine -l-SOyN CaHuN (CE1): L CHzCH(CzH5)C4H9 4 copper phtlialocyanine 10. 0 H ll /N\ /C\ I SOzNHCaHoN(CeH1s)CaHoN(CH:)a \C/ N/ ll H O opper tetraphenylphthalocyanine CHCHUJIHO 04H0 HiCHUxHCAHB CH: t a l CHg-C--tlH-GNH W N=Nsomnomuzolmmonm CH:CH(C:H)C4H 2 CH; o 0 l CH -ii-g-ci-g-Q-l 1 n" (n) H ClnHn ihre-@ i-N-Cim-N-cmNwzHm o 0 CHraaasQll i 1 a gl) (ImHn N=NN-CQH.N C,H Z o 16. o 1l C r -somncanulcsmmomh /CH \N L omcmmnocu, 1 2 C Il o 17. CH3 CH: CH; CH:

/o\ /C (l /o=oHCH=CH-C\ C1- If I. CH; *CH3 18. Alcian Blue SGN Color Index designation-Ingrain Blue 1 19. Alcian Yellow Color Index designation-Ingram Yellow 1 20. Carbacryl Brilliant Blue 3G Color Index No. 51005 (lCzHs /N\ C1- (CIHOIN N(C2Hi)a Table I shows the results obtained with various dyestuff combinations within the scope of this invention, following the abovementioned procedures. Results are evaluated as excellent, good, fair or poor, representing increasing evidence of undesirable color over the density scale. Examples 28 and 29 illustrate the poor'results observed with representative conventional cationic dyestuffs.

TABLE I Example Dyestuffs Density scale 2, 3 Excellent. 1, 7 Do. 2, 7 Do. 1, 8 Do. 2, 8 Do. 1, 9 Good. 2, 9 Excellent 2, 10 Do. 3, 10 Do. 1, 11 Do. 3, 11 Do. 6, 11 Do.

1, l2 D0. 3, 12 Do. 6, 12 Good. 1, 13 Do. 3, 13 Excellent. 6, 13 Do. 1, 14 D0. 3, 14 Fair. 6, 14 Excellent. 1, 15 D0. 3, 15 Do. 6, 15 Fair. 2, 16 Good. 3, 16 Do. 6, 16 Fair.

17, 18 Poor.

FIGURES l-4 illustrate the unusually smooth absorption curves obtained with the combination of three representative dyestufs of this invention and, for purposes of comparison, the absorption curves of the individual dyestuffs using a 0-3 neutral density wedge. FIGURE l is a plot of density versus rela-tive log exposure for the blue absorption of 0.75 weight percent yellow dyestulf No. 2, for the green absorption of 0.75 weight percent magenta dyestuff No. 1, and for the red absorption of 0.5 weight percent cyan dyestul No. 3. The exposure was approximately 5 seconds at 100 foot candles with a development time of .3 second and development voltage of 75 volts D.'C., anode spacing 'V2-inch from copysheet surface. FIGURE 2 shows a similar series of runs with the same dyestuir, using a development time of 1.2 seconds. From FIGURES 1 and 2 will 'be seen that the individual absorption characteristics of the three dyestuis differ quite markedly. FIGURES 3 and 4 are plots of density versus relative log exposure for the same dyestufls after electrodeposition from admixture, the dyes in FIGURES 3 and 4 being obtained with development times of .3 and 1.2 seconds, respectively. FIGURES 3 and 4 show the coincidence of the red, blue and green absorption curves for the three component dye mixture and verify the remarkably similar plating characteristics and resulting neutral rendition of the gray scale.

Various other embodiments of the present invention will be apparent to those skilled in the art without departing from the scope thereof.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electrolytic electrophotographic developer `which comprises `at least two dyestuls of the formula:

wherein D is a chromogenic radical, R is an ralkyl radical having from 6 to 12 carbon atoms, R" is methyl or ethyl, n is 2 or 3 and p is 0 or 1, which dyestuffs are soluble in water at a pH below about 6 and Kare insoluble at a pH above 7.

2. The developer of claim 1 wherein D is a chromogenic radical of the azo, anthraquinone, anthrapyridone, phthalocyanine, quinacridone, thioindigo or xanthene type.

3. The developer of claim 1 wherein said dyestuils are in amine salt form.

4. The developer of claim 1 having a cyan, a magenta and a yellow dyestuif in a proportion suicient to reproduce a gray scale in electrolytic electrophotographic development.

5. In an electrolytic electrophotographic process the improvement which comprises using a developer containing at least two dyestuifs of the formula wherein D is a chromogenic radical, R is an alkyl radical having from 6 to 12 carbon atoms, R' is methyl or ethyl, n is 2 or 3 and p is 0 or 1, which dyestutfs are soluble in water at a pH below about 6 and are insoluble at a pH above 7.

6. The process of claim 5 in which said dyestulfs include a cyan dyestul, a magenta dyestu and a yellow dyestulf in a proportion suicient to reproduce a gray scale in electrolytic electrophotographic development.

References Cited UNITED STATES PATENTS 3,010,883 11/1961 Johnson et al 204-18 3,172,826 3/1965 Tulagin et al. 204-18 3,172,827 3/1965 Tulagin et al. 204-18 IOHN H. MACK, Primary Examiner.

T. TUFARIELLO, Assistant Examiner.

UNTTED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,436 ,321 April 1 1969 Donald K. Meyer et al It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

C01umn 2, une 11, "D-[NH(CHZ)n]p-NH(CH2)mNH/2" Shoud read D[NH(cH2)n]P-NR(CH21mNR/Z co1umn 3, lines 19 1;@ 30, that portion of the formula reading should read same column 3 lines 55 to 57 that portion of the formula reading should 4read 2 2-4 Column 6 lines 13 and 34 "ethyl each occurrence should read ethyl, m is 2 or 3,

Signed and sealed this 14th day of April 1970 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

1. AN ELECTROLYTIC ELECTROPHOTOGRAPHIC DEVELOPER WHICH COMPRISES AT LEAST TWO DYESTUFFS OF THE FORMULA: 